Seat base



FIG. 1 is a front perspective view of a seat base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right elevational view thereof;

FIG. 5 is the left elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken away symbols, in FIGS. 2, 3, 4, and 5 of the drawings, indicate the appearance of any portion of the article between the break lines forms no part of the claimed design. 

CLAIM The ornamental design for a seat base, as shown. 